The present invention relates to a vacuum system for the treatment of work pieces having an evacuatable treatment chamber in whose central axis a low voltage arc discharge arrangement is disposed and at least one coating source attached to one lateral wall of the treatment chamber, as well as a work piece support on which work pieces can be mounted.
It is known in the art of vacuum coating to perform cleaning and/or heating steps for various vacuum treatment processes before and/or after vacuum coating. Such steps are particularly necessary in order to give a deposited layer a good adhesive strength. This is especially important for applications where work pieces, particularly tools and parts subject to high mechanical stresses, are to be coated with a wear-resistant hard coating. Such coatings are often used in making tools, for example drills, milling cutters, and shaping tools, and in making parts such as toothed gears, needles for injection nozzles, cup tappets, cam shafts, and other fast-moving or highly-stressed parts that are exposed to particularly high mechanical and abrasive stresses. An extremely good adhesion with the base is therefore a prerequisite for serviceable, economical use. A proven method of pre-treating such work pieces is, on the one hand, heating, particularly with electron bombardment, as well as etching using ion etching or sputter etching. Heating using electron bombardment from a plasma discharge has, for example, is known from German Patent No. DE 33 30 144. A plasma discharge path can also be used to produce heavy noble gas ions, for example argon ions, which can be accelerated out of that plasma onto the work piece or the substrate in order to cause sputter etching there, as described in German Patent No. DE 28 33 876. In addition to sputter etching, it is also known to operate plasma discharges with additional reactive gases, and to etch the work pieces with reactive chemistry, with mixed forms of such reactive etching and sputter etching also being possible.
In the aforementioned processes, the treatment chamber is often surrounded by an electromagnetic coil arrangement, preferably of the Helmholtz coil pair type, which makes it possible to further influence the plasma, for example to increase the plasma density or to concentrate the plasma, which causes a stronger ion bombardment, or to control the plasma distribution in the device, for example by changing the coil currents during plasma treatment and the like.
In all of these pretreatment processes, the work piece surface is prepared in such a way that the subsequent coating will adhere well to the base. In producing a plasma in the aforementioned treatments, a low voltage arc discharge is disposed along the central axis of the treatment chamber, with the work pieces being disposed at a specific distance from such central axis and along a cylindrical surface. The coating is then done by means of thermal evaporation or cathode sputtering, or mixed forms thereof, such as arc evaporation. Depending on process control, an additional ion bombardment can be produced during coating by a corresponding substrate bias, which is known by the term “ion plating.”
The above-described method has the advantage that large ion flows can be produced, with lower particle energy, from the low voltage arc discharge, and therefore the work piece can be treated gently. However, the need to arrange the work pieces to be coated so that they can be moved around a device attached centrally in the system for ignition of a low voltage arc, which is necessary in such processes, results in a relatively complex mechanical structure. For example, in current practice, parts to be coated are often fastened on individual work piece holders that are disposed symmetrically around the system axis, or rotatably mounted on carousel-like work piece supports. Moreover, to carry out the various process steps, different electrical potentials must be applied to the centrally disposed anode and the individual work piece holders (or the work piece support), and these components must be electrically insulated from each other and additionally from the grounded system. In some instances, it is necessary to provide additional electrical lead-throughs into the treatment chamber for temperature sensors or other measurement devices. Based on the complex mechanical and electrical requirements described above, known industrial equipment used to simultaneously coat a large number of parts (or to coat a smaller number of individual heavy parts) include work piece holders or carousel-like work piece supports that are connected rotatably with the vacuum chamber (typically, with the bottom of the vacuum chamber; however, in such known systems, the work pieces (and/or the work piece supports) can not be simply separated from the vacuum chamber. Therefore, loading and unloading of the work pieces through a lateral opening is consequently difficult, especially due to the centralized position of the low voltage arc discharge arrangement.
Accordingly, in large-scale industrial applications, an arrangement was chosen in which the bottom of the evacuation chamber, including the work piece support mounted thereto, is lowered away from the rest of the evacuation chamber during loading/unloading operations, either hydraulically or using spindle drives. Alternatively, it would be conceivable to leave the bottom of the evacuation chamber fixed in place, and to instead raise the balance of the evacuation chamber upward. Common to both such arrangements is the detrimental need to provide all supply lines (such as cold water and electricity) that are connected to the movable chamber bottom (or to the movable chamber, in the case of the alternate arrangement) in a costly movable design. The necessarily larger vertical height of such devices, and the longer down-time of such devices during loading and unloading operations, are also uneconomical.
In an effort to address such disadvantages, U.S. Pat. No. 5,709,784 discloses a system that is particularly appropriate for large-scale industrial mass production. The apparatus described in the '784 patent discloses PVD (physical vapor deposition) devices with low voltage arc discharge systems wherein the processing width for the work pieces can be up to 1,000 mm. and more, and which include simplified front loading and unloading of the work pieces. To achieve that goal, that apparatus disclosed in the '784 patent includes at least one low voltage arc discharge system that is attached laterally to the evacuation chamber, extending generally parallel to a moveable work piece support. However, while this asymmetrical arrangement of the low voltage arc discharge system provides handling advantages of the work pieces in comparison with a centralized arrangement of the low voltage arc discharge system, such handling advantages are offset by limitations imposed by geometrical considerations.